D-150A

I have a D-150A - early model (1975?) that has faithfully driven my Crown ES-212 electrostatic speakers for many years. (How many pairs of *those* units are still out there?!?!)

Just recently, the left channel has started sounding distorted, after power up. However, after a while, the problem seems to clear up.One local technician I spoke with (who seems to have some familiarity with the older Crown amps) told me that the problem is likely an "op-amp" that's going bad.

Opinions? If it is, in fact, an op-amp, are the parts still available? Cost? I'd love to upgrade to a newer Crown amp, but frankly the $$ just isn't there.

Also, just out of curiosity, are there any parts left for the electrostatic speakers? (Probably not, but hey...can't hurt to ask!!)

Stan, The op-amp could cause this. The item is a UA739 op-amp Crown part number C 3231-5 ($7.55 from parts dept.). Also, cracked solder connections on the driver transistors or poor ground connections on the pots or the input jacks. Crown does still repair these amplifiers. The service manual is available in pdf format as well.http://www.crownaudio.com/gen_htm/legacy/legacamp.htm

I have been at Crown for 16 years and unfortunately the Speaker parts were long gone before I started working here.

QUOTE(Video4Him @ May 10 2005, 10:35 PM)

I have a D-150A - early model (1975?) that has faithfully driven my Crown ES-212 electrostatic speakers for many years. (How many pairs of *those* units are still out there?!?!)

Just recently, the left channel has started sounding distorted, after power up. However, after a while, the problem seems to clear up.One local technician I spoke with (who seems to have some familiarity with the older Crown amps) told me that the problem is likely an "op-amp" that's going bad.

Opinions? If it is, in fact, an op-amp, are the parts still available? Cost? I'd love to upgrade to a newer Crown amp, but frankly the $$ just isn't there.

Also, just out of curiosity, are there any parts left for the electrostatic speakers? (Probably not, but hey...can't hurt to ask!!)

Stan, The op-amp could cause this. The item is a UA739 op-amp Crown part number C 3231-5 ($7.55 from parts dept.). Also, cracked solder connections on the driver transistors or poor ground connections on the pots or the input jacks. Crown does still repair these amplifiers. The service manual is available in pdf format as well.http://www.crownaudio.com/gen_htm/legacy/legacamp.htm

I have been at Crown for 16 years and unfortunately the Speaker parts were long gone before I started working here.

QUOTE(Video4Him @ May 10 2005, 10:35 PM)

I have a D-150A - early model (1975?) that has faithfully driven my Crown ES-212 electrostatic speakers for many years. (How many pairs of *those* units are still out there?!?!)

Just recently, the left channel has started sounding distorted, after power up. However, after a while, the problem seems to clear up.One local technician I spoke with (who seems to have some familiarity with the older Crown amps) told me that the problem is likely an "op-amp" that's going bad.

Opinions? If it is, in fact, an op-amp, are the parts still available? Cost? I'd love to upgrade to a newer Crown amp, but frankly the $$ just isn't there.

Also, just out of curiosity, are there any parts left for the electrostatic speakers? (Probably not, but hey...can't hurt to ask!!)

I just repaired a D150 with the same problem you are describing.It was just an electrolytic Cap that had opened up. I don't remember exactly which one it was, but there are only three on the pre-amp board. I think it was the 10uF. Chech that out while your in there.

QUOTE(Video4Him @ May 13 2005, 06:45 AM)

Thanks a bunch. I'm going to do a bit more troubleshooting and probably order that part.

I just repaired a D150 with the same problem you are describing.It was just an electrolytic Cap that had opened up. I don't remember exactly which one it was, but there are only three on the pre-amp board. I think it was the 10uF. Chech that out while your in there.

QUOTE(Video4Him @ May 13 2005, 06:45 AM)

Thanks a bunch. I'm going to do a bit more troubleshooting and probably order that part.

Thanks for the tip... I replaced the dual op-amp. Didn't fix the problem entirely.There was improvement, but still some distortion on power-up. At least the part was cheap. Now if I can just figure out which part it is you're talking about!!

Thanks for the tip... I replaced the dual op-amp. Didn't fix the problem entirely.There was improvement, but still some distortion on power-up. At least the part was cheap. Now if I can just figure out which part it is you're talking about!!

Stan

Sorry not to have picked up on this thread earlier.

In my experience it is very very rare for an op-amp to fail on a D150/A or DC300A etc.

It sounds more like a component deterioration problem within the current source for the voltage amplifier sections of which the 10uf capacitor (Circuit Ref. C5) previously mentioned is indeed part thereof. This is connected to the two small signal transistors that share a common heatsink on the PCB.

The easiset thing to do is measure the DC voltage across the 10V zenner diode that this capacitor goes in parrallel with. This should be (not surprisingly!) 10V but I expect that it will probably be between 7 and 9 instead. If so, the best thing to do in my experience is to replace the 10uf 63V cap, the zenner diode and (if you can get a suitable one) the series 10uf 150V capacitor that feeds this network from the power transformer/rectifier (Circuit Ref. C4).

The problem is a common one with DC300As that have been in service for some time but because the circuit is very similar on the D150/A it turns up there too.

I have a D150A that has been in storage 10 yrs or so ,(A SHAME I KNOW BUT ...) The right channel IOC indicator LED stays on all the time ,I havent tried sending a signal thru it yet .I was just wondering if anyone knew of some things I could try before sending it back to Mommy for repairs .I have limited test equipment ,but a decent background in electronics .Any help would sho be appreciated .... Sloan

I have a D150A that has been in storage 10 yrs or so ,(A SHAME I KNOW BUT ...) The right channel IOC indicator LED stays on all the time ,I havent tried sending a signal thru it yet .I was just wondering if anyone knew of some things I could try before sending it back to Mommy for repairs .I have limited test equipment ,but a decent background in electronics .Any help would sho be appreciated .... Sloan

I would get it to a service center as there is little you will be able to do with limited test equipment.However if you would like to attempt repair on your own the Service Manual is available as a free downloadable .pdf file at: http://www.crownaudio.com/gen_htm/legacy/legacamp.htm